The 21-year-old American marked a 6-1, 6-2, 7-6 fourth- round win against Andrew Foster, the world No 332 from Stoke, by rounding on partisan spectators on Court 14 and hitting a ball into the crowd before making a hasty departure.
Later, Sampras denied that he had used an expletive to the crowd. 'I said 'Thank you very much and God bless you'. Hasta la vista and out,' he said. 'The crowd was very vocal and I was excited at winning a pretty tense match and showed some emotion. I don't show much emotion and when I do people are surprised.'
A spokeswoman for Alan Mills, the Wimbledon referee, said later: 'Nothing untoward has been reported on the Sampras match, but it will be investigated tomorrow morning.'
Sampras, who idolises the exemplary Rod Laver, normally is a quiet competitor content to let Agassi grab the headlines. Yesterday, the former United States Open champion allowed himself to be affected by the raucous support which accompanied Foster's recovery in the third set. The Briton lost the tie- break, 8-6.
The American called for the trainer to massage his shoulder during three consecutive change-overs early in the third set. The injury was a recurrence of the problem that threatened his participation at Wimbledon.
Agassi, the defending champion, came unscathed through what was supposed to be his moment of truth against the serving power of Richard Krajicek. The Dutchman recovered from a nervous start to his Centre Court debut, but failed to take his chances to extend the contest. Agassi won, 7-5, 7-6, 7-6.
Two other Americans, Jim Courier and Todd Martin, also meet in the quarter-finals. Courier subdued a bad-tempered Wayne Ferreira, defeating the South African, 4-6, 7-6, 7-5, 6-3, and Martin edged out a compatriot, David Wheaton, 6-4, 5-7, 5-7, 7-5, 6-3.
Stefan Edberg continued his progress through the land of the unseeded, defeating the American Richard Matuszewksi in straight sets. The second seed now plays Cedric Pioline, of France, ranked No 23, who eliminated Australia's Wally Masur, 8-6 in the fifth set.
Top of the bill tomorrow is the German Open between Boris Becker and Michael Stich, a re- run of their match on the Centre Court in 1991, only three rounds earlier. The contest was made possible by Becker's ability to overpower Henri Leconte, 6-4, 6-4, 3-6, 6-3, and Stich's grass- court play against Petr Korda, which enabled him to defeat the Czech, 7-6, 6-4, 7-6.
It has taken Stich the best part of two years to grow accustomed to the celebrity that goes with the Wimbledon crown, while the gleam in Becker's eye shows how keen he is to add to his three triumphs.
Whatever Stich decides to do after tennis, he is unlikely to qualify as a fairground barker. Short of crying 'don't roll up]' he could hardly have deflated the hype being blown into tomorrow's confrontation more effectively. 'It's probably going to be a very boring match,' he said, pointing out that their six previous contests have been won in straight sets, three apiece. This includes their Wimbledon final. 'All the matches we've played were normally very easy for one or the other,' Stich said.
In a fashion that would win the approval of the World Wrestling Federation, some of the best bouts between the Germans have been out of the ring.
There was the spat last year over the Olympic doubles partnership, which ended in cheers when the pair lifted gold in Barcelona, and a Davis Cup row earlier this year, after Becker declined to play in the opening round, hinting that he might fancy a recall later.
All that is behind them, it appears. 'There's no relationship,' Stich said. 'We're both tennis professionals, and that's about it. I don't dislike him. I always give him a lot of credit for what he achieved in tennis. But there are not too many things that we have in common. I congratulated him when he came in now, but we don't talk about our daily problems.'
Becker concurred. 'We have played each other many times. We know each other quite well. Friends we are not, but we also are not enemies.'
While there is not sufficient evidence to suggest a feud, there is no doubt about the keenness of the rivalry. Asked if his loss to Stich was one of the most painful memories of his nine previous visits to Wimbledon, Becker replied: 'Yes, it was. Absolutely.'
Stich also won their most recent encounter, on grass at London's Queen's Club in the quarter-finals of the Stella Artois Championships a fortnight ago. 'Presumably he will have it in the back of his mind that I beat him twice on grass, and for sure that's a little advantage for me,' Stich said. 'But for sure he's more motivated than he was at Queen's'
Becker, the unseeeded Wimbledon sensation of 1985 after winning the Stella, nowadays tends to treat himself to a smile when he sees his Wimbledon rivals approaching peak form at Queen's. 'I was about 75 per cent there,' he said. 'Now I would say I'm 90 per cent to 95 per cent. After the match at Queen's, somebody told me that whoever won the first set went on to win the whole match. Let's see what happens tomorrow.'
The more distant Becker's triumph at the 1991 Australian Open has become, the more frequently doubts have been expressed about his ability to raise his game for the seven matches over the best of five sets required to win a Grand Slam event.
'It's not up to me to say whether his best days are gone or not,' Stich said. 'I think he's still capable of playing very good tennis, as he shows right now. But the biggest success he had was in the past, there's no question about it. His Grand Slam record over the last two years is not that great compared to the Grand Slam record he had before. . . There are players coming up who are playing much better than maybe five years ago.'
Becker took a positive view on the subject. 'I'm trying to change it this week,' he said. 'I would say it goes in stages. You have a couple of good years in the Grand Slams, and then you have a couple of bad years. Sometimes you don't have the answer all the time. If you did, you would be Einstein.'
----------------------------------------------------------------- MEN'S SINGLES QUARTER-FINAL LINE-UP ----------------------------------------------------------------- P SAMPRAS (US) v A AGASSI (US) B BECKER (Ger) v M STICH (Ger) T Martin (US) v J COURIER (US) C Pioline (Fr) v S EDBERG (Swe) -----------------------------------------------------------------
Brush-off for Leconte,
Order of Play, page 31